“It has been a tough flu season,” and may be only half over, said Dan Jernigan, director of the CDC’s influenza division.

While the CDC gets reports of flu deaths among children — up to 37 now — the biggest flu impact has been on people over age 65, followed by those ages 50-64, Jernigan said.

Flu trackers do not keep exact counts of adult deaths, but flu hospitalizations are higher among people in their fifties and early sixties this year than among young children, who usually are hospitalized at a rate only surpassed by the over-65 age group, he said.

“Baby boomers have higher rates than their grandchildren right now,” he said.

The reason for year to year age shifts are complex, but can include vaccination rates and the mix of viruses in circulation.

Still, “we expect there will be additional reports of pediatric deaths, similar to what we’ve seen in other severe seasons,” Jernigan said. He noted that in the 2014-2015 flu season, 148 child deaths were reported.

Last year, the number was 110, and the year before that, it was 92. In 2009-2010, the country had a rarer “pandemic,” in which a new flu virus took an especially high toll on children, killing 288.

Jernigan said the current season looks most like 2014-2015, when 34 million people got the flu, 710,000 were hospitalized and an estimated 56,000 died.

One unusual feature of this year’s flu is that it has stayed widespread across the country for three weeks running, instead of popping up in one region and then another. Geographic spread does not indicate severity, but as of Jan. 20, 39 states were still reporting high levels of flu-like illnesses. And 6.6% of people seeing doctors anywhere in the country had flu-like symptoms — the highest that measure has been since the pandemic year nearly a decade ago, Jernigan said.

There were some signs of improvement in certain areas, he said. Notably, he said the flu onslaught may have peaked in hard-hit California.

Jernigan and CDC director Brenda Fitzgerald repeated calls for people to protect themselves and others by getting the flu vaccine, staying home when they are sick and washing their hands.

The very young, the very old, pregnant women and people with underlying conditions — such as asthma and heart disease — are at highest risk from flu and should seek treatment if they get sick, Jernigan said.